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Abstract
Efficient algorithms for timing, carrier frequency and phase recovery of Nyquist and OFDM signals are introduced and experimentally verified. The algorithms exploit the statistical properties of the received signals to efficiently derive the optimum sampling time, the carrier frequency offset, and the carrier phase. Among the proposed methods, the mean modulus algorithm (MMA) shows a very robust performance at reduced computational complexity. This is especially important for optical communications where data rates can exceed 100 Gbit/s per wavelength. All proposed algorithms are verified by simulations and by experiments using optical M-ary QAM Nyquist and OFDM signals with data rates up to 84 Gbit/s.
Highlights
Clock and carrier recovery are crucial tasks when coherently receiving data transmitted over optical links
#205525 - $15.00 USD Received 3 Feb 2014; revised 27 Mar 2014; accepted 27 Mar 2014; published 10 Apr 2014 (C) 2014 OSA. From these results we conclude that the proposed mean modulus algorithm (MMA) and the constant modulus algorithm (CMA) perform well, leaving the MMA with the advantage of less computational complexity except for orthogonal frequency division multiplexing (OFDM) timing synchronization where the complexity is virtually same for both algorithms
With the resulting coefficients ci′k, we evaluate the mean power algorithm (MPA), the MMA, the CMA, and the constant power algorithm (CPA) algorithms according to Eq (13)–(16) as a function of the frequency offset ν normalized to the subcarrier spacing Fs
Summary
Clock and carrier recovery are crucial tasks when coherently receiving data transmitted over optical links. Timing recovery (: clock recovery) and carrier recovery methods can be grouped into feedforward and feedback techniques In both cases, the actual value of frequency, phase or sampling time has to be estimated. One way to find the proper timing information is to use square-law detectors [6] [7], i.e., the modulus of the received time domain signal is squared This algorithm is not applicable for Nyquist pulses with a small roll-off factor β ≈0 [6] [7]. The Viterbi-Viterbi method provides both the carrier frequency and the carrier phase offset For multicarrier signals such as with OFDM, the Schmidl-Cox algorithm [12] is widely used. We discuss the experimental setup and apply the algorithms to OFDM signals with 128 SCs and Nyquist pulses with various roll-off factors β and data rates of up to 84 Gbit/s
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